Tube still and furnace construction



y 1934' J. s. WALLIS 58,732

TUBE STILL AND FURNACE CONSTRUCTION Filed July 9, 1931 1000-0- OOOOOOOO-OO INVENTOR. John 5 Wa/h:

A TTORNE 'Patented May 15,, 1934 UNITED STATES 1,958,732 I runs STILL AND FURNACE CONSTRUCTION John s. Wallis, New York, N. Y., assignor to- Alco Products, Incorporated, New York, N. Y., a corporation of Delaware Application July 9, 1931, Serial No. 549,730 I 4 Claims.

This invention relates to improvements in tube stills and furance construction and refers more particularly to a still adaptable for the use of processing or heating of hydrocarbon oils.

The novelty of the invention lies principally in the arrangement of the tubes within the furnace, the varying of the diameter of the tubes as the oil flows therethrough in ,order to impose diiferential pressures in the different sections of the heat absorbing surfaces and in the connecting up of the tubes in order by bends, to reduce the friction and consequently the pressure drop of the oil during its travels therethrough.

The single figure is a longitudinal sectiontaken through the furnace. 1

The construction consistsof furnace walls 1, supporting a roof 2 and mounted upon suitable foundations 3. The furnaceconsists of a combustion chamber '4 and a convection or tube chamber 5 separated by a bridge wall 6. The combustion or heating gases are supplied to the furnace by the burning of a fuel by means of a gas or oil burner, diagrammatically shown at '7. The fuel burned within the combustion chamber 4 passes over the top of the bridge wall downwardly through the tube chamber and out through the flue 8. The heat absorbing surface consists of banks of tubes 9, 10, and 11. The medium to be heated, in this case oil, is intro- 80 tiuced through the inlet pipe 12 and is then passed are serially connected, thence through a transfer pipe 13 into the tube bank from which it is discharged through a. transfer pipe 14 and, after passing through the tubes in the bank 11, is directed through the transfer pipe 15 into the inlet end of the roof tubes 16, which tubes receive principally radiant heat from the combustion chamber. The tubes 16 are connected as are the convection tubes in the banks 9, 10 and 11 by 180 degree return bends. After passing successively through the tube 18, the oil is discharged through the pipe 17 into the tubes 18, which are horizontally positioned on the side walls of the furnace above the bridge wall and are connected by 90 degree bends. Also the tubes 18 are of a larger diameter than the tubes 16, which comprise the roof ban. This increase in size of the tubes, as well as the 90 degree bends. considerably reduces the friction imposed upon the fluids passing through the tubes as compared with the back pressure or friction which would retard the passage were the tubes of the same size as the tubes 16 and connected by 180 degree bends. After passing through the radiant absorbing surface.

successively through the tube bank 9 which tubes.

or tube bank 18, the oil is discharged through pipe 19 to an evaporator or to other stages of processing not shown.

The pressure drop throughlfan oil heating sur face is a function of the friction through the tubes and the friction through the return bends so that the friction through the return bends is considerably more than the total friction drop through the tubes. It is also a fact that with radiant and convection tube stills, that a pressure drop through the radiant section is relatively high, of the order of 75% of the total pressure drop, and the pressure drop through the convection banks or convection heat absorbing surface relatively low due to the fact that the oil in the convection banksbeing at a lower temperature, is almost entirely in the liquid phase, while the oil in the radiant bank, at higher temperature and considerably more vaporization percent, the pressure drop increases correspondingly with the increased vaporization.

Also when a vacuum is imposed uponthe evaporation end of a distillation system, it is desirable to carry back the reduced pressure into the heater as far as possible in order to procure evaporation of the oil at as low temperature as is feasible. This is desired in order to procure improved types of final products, principally lubricating oils, as overheating deteriorates the oil probably more than any other factor of the processing operation.

In order to accomplish the evaporation of the oil at as low temperatures as possible, it is desirable to reduce the friction and pressure necessary to pass the oil through the heater. A decided step in this direction has been made by the construction suggested in which the oil is passed through the convection heat absorbing surface or tube banks 9, 10 and 11 in an opposed direction to the combustion gases passing therethrough. In this surface the oil is raised to a temperature wherein no substantial vaporization is produced. It is then passedto. the radiant heat absorbing surface in the form of roof tubes of a size somewhat larger than the convection tubes. Finally, the oil is passed to the radiant section or heat absorbing surface which comprises the side wall tubes which are of considerably greater diameter In the design of tube stills for operation of vacuum fractionating towers, it is recognized that eter-in the latter passes of the furnace.

it has been the practice to increase the tube diam- This is done to permit subatmospheric pressure to carry back into the tube still, permitting the maximum vaporization and the maximum latent heat of vaporization by direct fire. If this were not done and the tube still outlet was maintained at atmospheric pressure or slightly above, a relatively small amount of vaporization would take place in the tube still. It would then be necessary to heat the oil to a higher temperature and absorb latent heat of vaporization from the sensible heat of the liquid in the flash chamber of the vacuum fractionating tower.

With the conventional design of furnaces used in connection with'vacuum distillation, the tube still outlet is maintained at approximately 300 millimeters absolute pressure. Approximately ten tubes back in the furnace, the pressure is very nearly atmospheric and beyond that point the pressure is above atmospheric. If it were possible to reduce the friction through the headers, obviously this vacuum could be maintained further back in the furnace, even to the extent of twenty tubes instead of ten tubes, as suggested. As a specific instance, a vacuum tube still was built which had five inch tubes in the upper roof tubes and six inch tubes in the .side roof tubes, the flow through the furnace being first through the convection bank, thence through the upper roof tubes, thence through the side roof tubes and finally through the transfer line to the fractionating tower. This tube still was operated at an outlet temperature of 790 F. and 300 millimeters absolute pressure. Ten tubes anterior of the transfer line, the pressure was 760 millimeters from the sensible heat of the liquid. By reducing of construction.

the friction drop through the headers or bends by means of which the tubes are connected, and by use of degree bends, obviously the vacuum can be taken much further back into the still and overheating of the oil above the outlet temperature considerably reduced and eliminated.

What is claimed then to be novel is to reduce and carry back the vacuum pressure considerably farther into the heater by connecting up the latter passes of the radiant section by 90 degree bends and connecting a radiant section or heat absorbing surface of this character with a convection section or aseparate radiant and convection section such as is shown in the drawing.

At 20 in the drawing is shown a bank of heating tubes adapted to generate steam or superheated steam for processing the oil. This particular bank of tubes forms no part of the present invention but is conventional practice in this type ing one side of said combustion chamber, a plurality of heat absorbing elements positioned behind said bridge wall, adapted to be heated main ly by the convection heat component of said gen erated heat, a plurality of heat absorbing elements adapted to be heated mainly by the radiant heat component of said generated heat,

said radiant heat absorbing elements being of larger cross section than said convection heat absorbing elements, said radiant heat absorbing elements comprising two groups, one of said groups being'disposed in a plurality of vertical banks, the other ofsaid groups being disposed in a horizontal-bank, the elements in said vertical banks being of larger cross section than the elements in said horizontal bank and being connected in series solely by 90 degree bends.

2. A furnace adapted for the pyrolytic processing of hydrocarbon oils comprising in combination a housing, a combustion chamber within said housing, means for generating heat within said combustion chamber, a bridge wall defining one side of said combustion chamber, a plurality of heat absorbing elements positioned behind said bridge wall, adapted to be heated mainly by the convection heat component of said generated heat, a plurality of heat absorbing elements adapted to be heated mainly by the radianhheat component of said generated heat, said radiant heat absorbing elements being of larger cross section than said convection heat elements, said radiant heat absorbing elements comprising two groups, one of said groups being disposed in a plurality of vertical banks, the other of said groups being disposed in a. horizontal bank, the elements in said vertical banks being of larger cross section than the elements in said horizontal bank and being connected in series solely by 90 degree bends, said convection heat absorbing bank, said horizontal radiant heat absorbing bank and said vertical radiant heat absorbing bank having their respective elements connected in series, an inlet for the material to be processed communicating with an element of the convection heat absorbing bank, and an outlet for the material to be processed from an element in the vertical radiant heat absorbing bank, whereby the material to be processed flows through the convection bank, the horizontal radiant heat bank and the vertical radiant heat bank in successlon.

3. A furnace having a roof wall and side walls adapted for the pyrolytic processing of hydro- 1,20 carbon oils including in combination a tube bank to be heated by ubstantially only convection heat, two tube nks positioned to ,be heated mainLv by radiant heat; one of sa radiant heated banks positioned adjacent the roof wall and constituting a ceiling bank, the other radiant heated bank positioned adjacent the side walls and constituting a side wall bank, connections between said banks whereby fluid introduced thereto passes successively through the convectionbank, the ceiling bank and the side wall bank said side wall bank comprising tubes of larger diameter than the tubes of said ceiling bank.

4. A furnace-having a roof wall and side walls adapted for the'pyrolytic processing of hydrocarbon oils, including in combination a tube bank heated substantially only by convection heat, two tube banks positioned to be heated mainly by radiant heat; one of said radiant heated banks positioned adjacent the roof wall and constituting, a ceiling bank, the other radiant heated bank positioned adjacent the side walls and constituting a side'wall bank-connections between said banks whereby/fluid introduced thereto passes successively through-the convection bank, the ceiling bank and the side wall bank, the tubes of I the respective banks being of progressively greater diameters.

.. JOHN S. WALLIS. 

